Compositions to stabilize asphaltenes in petroleum fluids

ABSTRACT

Compositions may include those of the formula: (I) wherein R1 is an alkyl chain having a carbon number in the range of greater than 40 to 200, R2 is a multiester, R3 is hydrogen, an ion, or an alkyl chain having a carbon number in the range of 1 to 200, m is an integer selected from 0 to 4, and n is an integer selected from the range of 0 to 4, wherein the sum of m and n is 1 or greater. Compositions may include a reaction product of a polyisobutylene-substituted succinic anhydride and a hydroxy-functional dendrimer, wherein the molar ratio of polyisobutylene-substituted succinic anhydride to hydroxy-functional dendrimer is within the range of 10:1 to 30:1.

BACKGROUND

The stability of produced crude oil may change in response to variationsin pressure, temperature, or composition, which may increase thetendency of certain components such as asphaltenes to agglomerate intolarger particles and/or form insoluble residues. Asphaltenes are organicheterocyclic macromolecules which may be found in crude oil and aregenerally stabilized by maltenes and other compositions under reservoirconditions.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments of the present disclosure are directed tocompositions that include the formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200, R2 is a multiester group, R3 is hydrogen, an ion, or an alkylchain having a carbon number of 1 to 200, m is an integer selected from0 to 4, and n is an integer selected from the range of 0 to 4, whereinthe sum of m and n is 1 or greater.

In another aspect, embodiments of the present disclosure are directed tocompositions that include a reaction product of apolyisobutylene-substituted succinic anhydride and a hydroxy-functionaldendrimer, wherein the molar ratio of polyisobutylene-substitutedsuccinic anhydride to hydroxy-functional dendrimer is within the rangeof 10:1 to 30:1.

In another aspect, embodiments of the present disclosure are directed tocompositions that include the formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200, R2 is a multiester group, X is —OR3 or —NR4R5 or —OM, wherein R3is an alkyl or aryl group having a carbon number of 1 to 200, R4 and R5are independently hydrogen or an alkyl, alkenyl, alkoxyalkyl, or arylgroup having a carbon number of 1 to 200; M is an alkali metal, alkalineearth metal, ammonium, alkyl-substituted ammonium, or aryl-substitutedammonium ion, each of m and n is an integer from 0 to 4, and the sum ofm and n is 1 or greater.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a hydroxy-functionaldendrimer, followed by conversion of any free carboxylic acid groupsfrom the anhydride to an acid salt, an ester, or an amide group.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a hydroxyalkylacrylate monomer, followed by radical-initiated polymerization of theresulting macromonomer and conversion of any free carboxylic acid groupsfrom the anhydride to an acid salt, an ester, or an amide group.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a polyol, especiallyglycerol, followed by conversion of any free carboxylic acid groups fromthe anhydride to an acid salt, an ester, or an amide group.

Conversion of free carboxylic acid groups from the anhydride to an acidsalt, an ester, or an amide group (after reaction of thepolyisobutylene-substituted succinic anhydride) unexpectedly prevents anundesirable reverse reaction in which the anhydride reforms and thehydroxy-functional dendrimer, hydroxyalkyl acrylate copolymer, or polyolis eliminated. The undesirable reverse reaction has been found to occurat the elevated-temperature conditions in which the compositions arenormally used for dispersing asphaltenes or inhibiting asphaltenedeposition.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1 and 2 are graphical representations of asphaltene inhibition asmeasured by percent average transmission as a function of time inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to methods and compositionsfor inhibiting the deposition of asphaltenes from hydrocarbon fluidswithin wellbores. In one or more embodiments, methods and compositionsin accordance with the present disclosure are directed to inhibiting ordispersing asphaltene deposition for topside and downhole oilfieldapplications. Treatment fluid compositions of the present disclosure maybe used in downhole and surface applications including dispersion ofexisting residues on wellbore equipment and wellbore surfaces, inaddition to inhibition of asphaltene precipitation during production andtransportation of various hydrocarbon fluids.

Asphaltenes may precipitate out of the oil, creating aggregates that mayentrain solids and other materials, which may initiate the formation ofsludges and other insoluble residues. Asphaltene deposits may accumulateon the surfaces of completions equipment and reservoir pore throats,which can lead to production impairment and other operational problemsincluding but not limited to, plugging of equipment, pressure loss,increased utility costs, lost production due to downtime, and downgradedproducts from insufficient feeds.

Asphaltenes are organic materials containing aromatic and naphthenicring compounds that may come in the form of polyaromatic or polycyclicstructures, and which may include a number of alkyl chains andheteroatoms such as nitrogen, sulfur and oxygen. In addition,asphaltenes may also include associated ions such as vanadium, nickel,and other metals. Asphaltenes are often described as a component of the“asphaltene fraction,” which contains a wide variety of heavy and polarmolecules from crude oils that are soluble in aromatic solvents, butinsoluble in normal alkane-based solvents such as pentane or heptane.

Asphaltenes exist as a colloidal suspension stabilized by aromaticresins in crude oil. The stability of asphaltic dispersions may dependin part on the ratio of resin to asphaltene molecules, which may be usedto estimate potential damage created by asphaltenes. During productionand transport of hydrocarbon fluids, asphaltenes may precipitate as aresult of pressure drop, composition changes, pressure depletion abovethe saturation pressure, temperature changes, shear from turbulent flow,intermixing of incompatible fluids or materials that break the stabilityof the asphaltic dispersion, and other parameters such as pH, solutioncarbon dioxide, water cut, electro-kinetic effects.

Asphaltene inhibitor and treatment fluid compositions in accordance withthe present disclosure may be used as additives that are provided tohydrocarbon mixtures to disperse asphaltene aggregates and/or preventflocculation of heavy hydrocarbons. Treatment fluids in accordance withthe present disclosure may be suitable for use in downhole environments,at the surface, and in pipelines used to transport hydrocarbons. In someembodiments, asphaltene inhibitors may be placed into a hydrocarbonproduction stream at any point, including within the wellbore, at thesurface of the well, and during transport of the hydrocarbon streamthrough pipelines or storage tanks.

Asphaltene inhibitor compositions of the present disclosure may be mixedwith hydrocarbon fluids either by batch treatment or by continuousinjection. In some embodiments, asphaltene inhibitors may be used as awellbore fluid additive, and in other treatment fluids such as squeezetreatments. Further, compositions in accordance with the presentdisclosure may inhibitor asphaltene agglomeration in both downhole andsurface applications, including at surface and downhole HPHT wellconditions. In some embodiments, treatment compositions may contain anasphaltene inhibitor combined with one or more aromatic solvents.

In one or more embodiments, treatments in accordance with the presentdisclosure may stabilize asphaltenes in production fluids, reducingand/or preventing asphaltene deposition, which may increase oilproduction and minimize the need for maintenance and cleaning. Withoutbeing limited by any particular theory, it is envisioned that compoundsin accordance with the present disclosure may mimic resin acids thatnaturally stabilize asphaltenes in the well by interacting with variousheteroatoms in the asphaltenes. Asphaltene inhibitors in accordance withthe present disclosure may also incorporate some degree of branching inthe molecular structure of the inhibitor, which may provide the sameinhibitory effects as linear asphaltene inhibitors without theassociated increase in viscosity.

In one or more embodiments, asphaltene inhibitors in accordance with thepresent disclosure may be a multiester asphaltene inhibitor. As usedherein, the term “multiester” is used to describe a molecule having twoor more hydroxy functional groups modified to contain two or more esterbonds to a molecule (or molecules) having one or more carboxylic acidgroups. Multiester asphaltene inhibitors in accordance with the presentdisclosure may include from 4 to 100 ester groups in some embodiments,and from 5 to 20 ester groups in other embodiments.

Multiester asphaltene inhibitors in accordance with the presentdisclosure may include: dendrimeric compounds branched with respect to ahydroxy-functional dendrimer, branched polymeric structures, oresterified polyols that may have some degree of cross-linking betweenthe polyol species prior to or following esterification to form themultiester. The asphaltene inhibitors of the present disclosure will bediscussed in the following sections with respect to the constituentreactants used to produce the final branched compounds.

Dendrimeric Asphaltene Inhibitors

In one or more embodiments, asphaltene inhibitors in accordance with thepresent disclosure may be prepared from the reaction of ahydroxy-functional dendrimer and an alkyl cyclic anhydride. As usedherein, the term “hydroxy-functional dendrimer” describes a dendrimericmolecule having two or more hydroxy groups. In some embodiments,hydroxy-functional dendrimer in accordance with the present disclosuremay have three dimensional macrostructure, which may be generational ortree-like that terminates in one or more hydroxy moieties. Branchedhydroxy-functional dendrimers may be symmetric with respect to a centralor quaternary carbon, or may be asymmetrical to some degree.

In some embodiments, dendrimeric molecules in accordance with thepresent disclosure may be prepared using convergent synthesis in whichmultiple branches are generated and grafted onto a polyalcohol coremolecule. Dendrimeric molecules in accordance with embodiments of thepresent disclosure may also be generated from divergent synthesismethods in which a polyalcohol core is reacted with a multifunctionalmolecule such as a hydroxy acid to prepare a dendrimer having one ormore generations. In one or more embodiments, the number of free hydroxygroups in the hydroxy-functional dendrimer may be tuned by controllingthe number of generations in the dendrimeric molecule, with increasednumbers of generations resulting in increased numbers of free hydroxygroups. Polyalcohol cores in accordance with the present disclosure mayinclude polyalcohols such as glycerol, trimethylolethane,trimethylolpropane, pentaerythritol, propylene glycol, butanetriol,inositol, erythritol, sorbitol, sugars such as mannitol, xylitol, andthe like, and other symmetric and asymmetric polyalcohols.Multifunctional molecules that may be used to construct dendrimericmolecules in accordance with the present disclosure include hydroxyacids such as 2,2-dimethylol propionic acid. In some embodiments,hydroxy-functional dendrimer may include commercially availablecompounds such as BOLTORN™ dendrimers, from PERSTORP (Malmo, Sweden),which is a family of dendritic polyols with large numbers of terminalhydroxy groups.

Hydroxy-functional dendrimers in accordance with the present disclosuremay have sufficient branching to possess at least 8 terminal hydroxylgroups, or at least 12 or 16 terminal hydroxyl groups in otherembodiments. The terminal hydroxyl groups of the hydroxy-functionaldendrimer of the present disclosure may be modified throughesterification with alkyl cyclic anhydrides, such as an alkyl succinicanhydride, to contain two or more ester bonds.

In some embodiments, dendrimeric asphaltene inhibitors in accordancewith the present disclosure may be prepared from a hydroxy-functionaldendrimer having a hydroxyl value, as determined by ASTM D 1957, withinthe range of 230 to 260 mg KOH/g. Dendrimeric compounds in accordancewith the present disclosure may also possess a weight average molecularweight within the range of 5,500 Da to 6,000 Da prior to reaction withone or more alkyl cyclic anhydride.

In some embodiments, dendrimeric asphaltene inhibitors may be amultiester having a number of ester bonds that range from 1 to 50.Depending on the total number of hydroxy groups available on thedendrimeric species, the ratio of the alkyl succinic anhydride to thehydroxy-functional dendrimer may range from between 1:1 and 50:1 in someembodiments, or from 1:1 to 11:1, where n is an integer describing thetotal number of hydroxy groups on the dendrimer, in particularembodiments.

In one or more embodiments, compositions in accordance with the presentdisclosure may include a compound of the formula:

wherein R1 is an alkyl chain having a carbon number in the range ofgreater than 40 to 200, R2 is a dendrimeric multiester, R3 is hydrogen,an ion, or an alkyl chain having a carbon number in the range of 1 to200, m is an integer selected from 0 to 4, and n is an integer selectedfrom the range of 0 to 4, wherein the sum of m and n is 1 or greater. Insome embodiments, R1 may be an alkyl chain having a carbon number withinthe range of 50 and 100, or within the range of 60 and 75, R3 may be H,the sum of m and n may be 1, and R2 may be a dendrimeric multiestercontaining between 8 to 50 ester groups.

In some embodiments, dendrimeric asphaltenes may have a weight-averagemolecular weight in the range of 900 Da to 100,000 Da, or in the rangeof 10,000 Da to 50,000 Da. Dendrimeric asphaltene inhibitors inaccordance with the present disclosure may include an R1 containing apolymer, including branched and linear polymers, composed of monomerssuch as ethylene, propene, butylene, isobutylene, or combinationsthereof. In some embodiments, dendrimeric asphaltene inhibitors maycontain a dendrimer moiety R2 containing a polyalcohol-based coreprepared from recurring generations of a polyol such as pentaerythritolor 2,2-dimethylolpropionic acid.

In one or more embodiments, dendrimeric asphaltene inhibitors inaccordance with the present disclosure may be prepared by reacting apolyisobutylene-substituted succinic anhydride with a hydroxy-functionaldendrimer. In some embodiments, the molar ratio of alkyl cyclicanhydride to hydroxy-functional dendrimer is within the range of 10:1 to30:1, or within the range of 15:1 to 25:1, or about 20:1. In someembodiments, the alkyl cyclic anhydride has a weight average molecularweight within the range of 500 Da to 5,000 Da, or within the range of800 Da to 3,500 Da. Dendrimeric asphaltene inhibitors in accordance withthe present disclosure may contain a reaction product of apolyisobutylene-substituted succinic anhydride and a hydroxy-functionaldendrimer, wherein the molar ratio of polyisobutylene-substitutedsuccinic anhydride to hydroxy-functional dendrimer is within the rangeof 10:1 to 30:1.

Polymeric Asphaltene Inhibitors

Asphaltene inhibitors in accordance with the present disclosure mayinclude “brush” or “comb” polymers produced by the reaction of an alkylsuccinic anhydride with a hydroxy vinyl monomer to prepare a“macromonomer” that is polymerized. In some embodiments, polymericasphaltene inhibitors may be prepared by reacting an alkyl cyclicanhydride with a polymer prepared from the polymerization of a “hydroxyvinyl monomer.” As used herein, a hydroxy vinyl monomer is a compoundhaving one or more hydroxyl groups and one or more polymerizablecarbon-carbon double bonds.

In one or more embodiments, asphaltene inhibitors may be a multiesterprepared from the esterification of a hydroxyl vinyl monomer having oneor more hydroxy groups. Hydroxy vinyl monomers that may be modified byan esterification reaction with an alkyl cyclic anhydride in accordancewith the present disclosure include acrylates, and equivalentmethacrylates of each of the following acrylates, such as hydroxyethylacrylate, hydroxypropyl acrylate, 1,3-butyleneglycol monoacrylate,1-bromo-2-hydroxypropyl acrylate, hexandiol monoacrylate,neopentylglycol monoacrylate, trimethylolpropane diacrylate,pentaerthyritol acrylate, dipentaerythritol acrylate, and the like.Other hydroxy vinyl monomers may include polymerizable monomerscontaining one or more hydroxy groups such as hydroxylbutyl vinyl ether,1,4-cyclohexanedimethanol mono vinyl ether, vinyl alcohol, allylalcohol, crotyl alcohol, p-vinylbenzyl alcohol, trimethylolpropanediallyl ether, N-methylolacrylamide, and the like.

In one or more embodiments, asphaltene inhibitors may be prepared from alinear or branched polymer having a number of free hydroxy groups towhich alkyl succinic anhydrides have been grafted on to the polymerbackbone to create polymer comb or polymer brush structure. The molarratio of the alkyl succinic anhydride to the hydroxy groups on thepolymer chain may range from between 1:1 and 50:1 in some embodiments,or from 1:1 to n:1, where n is an integer describing the total number ofhydroxy groups on the polymer, in particular embodiments. In someembodiments, hydroxy vinyl monomers may be combined with one or morecomonomers to produce a co-, ter-, or quater-polymer as needed to modifythe desired properties of the asphaltene inhibitor such as solubility,temperature stability, and net ionic charge.

In addition to polymers, copolymers, terpolymers, etc., prepared fromthe hydroxy vinyl monomers discussed above, hydroxy-containing polymerssuitable for reaction with alkyl cyclic anhydrides in accordance withthe present disclosure may also include partially hydrolyzed vinylacetate, partially hydrolyzed ethylene-vinyl acetate, partiallyhydrolyzed polyvinyl formate, and the like.

In one or more embodiments, a polyisobutylene succinic anhydride may bereacted with a 2-hydroxyalkyl acrylate or 2-hydroxyalkyl methacrylatemonomer to generate a macromonomer having available ethylenicunsaturation. Free radical-initiated polymerization of the macromonomermay then yield a comb polymer that may be used in the asphalteneinhibitor compositions described herein. In some embodiments, molecularweight may be limited by including one or more chain-transfer agentssuch as lauryl mercaptan in the reaction mixture during the free-radicalpolymerization step. The reaction to produce the comb copolymer isillustrated by the reaction of polyisobutylene succinic anhydride with2-hydroxyethyl methacrylate, followed by radical-initiatedpolymerization of the resulting macromonomer:

Polymeric asphaltene inhibitors in accordance with the presentdisclosure may have a molecular weight in the range of 10,000 to 200,000Da, or in some embodiments, may fall within the range of 20,000 to100,000 Da. As used herein, molecular weight refers to weight averagemolecular weight (M_(W)) unless indicated otherwise.

Polyol-Based Asphaltene Inhibitors

In one or more embodiments, asphaltene inhibitors may includemultiesters prepared from the reaction of an alkyl cyclic anhydride anda polyol. Polyols in accordance with the present disclosure may includehydroxy compounds having two or more hydroxyl groups such as glycerol,trimethylolethane, trimethylolpropane, pentaerythritol, propyleneglycol, butanetriol, inositol, erythritol, sorbitol, sugars such asmannitol, xylitol, and the like. In some embodiments, polyols may beoligomerized by etherification prior to reaction with alkyl cyclicanhydrides in accordance with the present disclosure in order tointroduce a degree of branching in the structure. In some embodiments,branching may also be introduced by reacting the product of the reactionbetween an alkyl cyclic anhydride and a polyol with an alkyl alcohol.

In one or more embodiments, asphaltene inhibitors may include a reactionproduct of polyisobutylene succinic anhydride (PIBSA) and glycerol:

In some embodiments, the reaction is performed such that at least someof the PIBSA is fully reacted with hydroxyl groups of the glycerol, thusenabling a greater degree of branching. In some aspects, the molar ratioof glycerol to PIBSA in the reaction mixture is within the range of 1:1to 5:1. In some aspects, the molar ratio of glycerol recurring units toPIBSA recurring units in the reaction product obtained is within therange of 1:10 to 10:1.

In one or more embodiments, an asphaltene inhibitor of the presentdisclosure may include an asphaltene inhibitor synthesized from anesterification reaction of a polyol and an alkyl succinic anhydridehaving a molar ratio of polyol to alkyl succinic anhydride will bewithin the range of 1:1 to 5:1, or in the range of 1.5:1 to 3.0:1.

Alkyl Cyclic Anhydride

In one or more embodiments, multiester asphaltene inhibitors may beprepared from the reaction of a polyhydroxy compound or polymerizablehydroxy compound and an alkyl cyclic anhydride. In one or moreembodiments, alkyl cyclic anhydrides may be selected from anhydridesprepared from the polymerization of a small-molecule unsaturatedcompound such as ethylene, propene, butylene, or isobutylene. In someembodiments, the molecular weight of the constituent alkyl chain of thealky cyclic anhydride may range from 500 Da to 10,000, 500 Da to 5,000Da, or from 800 Da to 3,500 Da. The cyclic anhydride component of thealkyl cyclic anhydrides may contain a cyclic anhydride moiety such assuccinic anhydride, glutaric anhydride, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, phthalic anhydride,norbornene-2,3-dicarboxylic anhydride, and naphthalenic dicarboxylicanhydride. In some embodiments, alkyl cyclic anhydrides may includepolyisobutylene succinic anhydride (PIBSA).

In some embodiments, alkyl cyclic anhydrides in accordance with thepresent disclosure may be of the general formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200; m is an integer selected from 0 to 4; and n is an integerselected from the range of 0 to 4, wherein the sum of m and n is 1 orgreater.

Upon the reaction between the alkyl cyclic anhydride and ahydroxyl-containing compound (such as those described above), anasphaltene may be generated. In some embodiments, the free carboxylicacid generated from the initial reaction of alkyl cyclic anhydride witha hydroxy functionalized species may be used as is or reacted furtherwith a second hydroxy functionalized species to form a second ester.

Asphaltene inhibitors in accordance with the present disclosure may beof the general formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200; R2 is a multiester; R3 is a covalent hydrogen, an alkyl chainhaving a carbon number 1 to 200, or a ion; m is an integer selected from0 to 4; and n is an integer selected from the range of 0 to 4, whereinthe sum of m and n is 1 or greater.

Asphaltene inhibitors in accordance with the present disclosure may beadded to a wellbore fluid formulation at a concentration that may rangefrom 1 ppm to 10,000 ppm of the wellbore fluid in some embodiments, andfrom 5 ppm to 5,000 ppm in particular embodiments.

In one or more embodiments, asphaltene inhibitors may be used inconjunction with one or more aromatic solvents that may increase thedispersion and/or inhibitory effects of the treatment. Aromatic solventsin accordance with the present disclosure may be combined with anasphaltene inhibitor prior to injection downhole or subsequent to theinjection of the asphaltene inhibitor or other wellbore fluid. Suitablearomatic solvents that may be used as a component of compositions inaccordance with the present disclosure include benzenes, alkyl benzenessuch as toluene, xylene, ethylbenzene, trimethyl benzene, cumene,mesitylene, combinations thereof, and the like. While a number ofsolvents are disclosed, it is also envisioned that other solvents may beselected that are miscible with petroleum fluids such as crude oil,condensates, diesel, and the like. In one or more embodiments, wellboretreatment compositions may contain one or more aromatic solvents at apercent by volume (v %) that ranges from 1 v % to 90 v %.

In some aspects, the asphaltene inhibitor compositions include compoundsof the formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200, R2 is a multiester group, X is —OR3 or —NR4R5 or —OM, wherein R3is an alkyl or aryl group having a carbon number of 1 to 200, R4 and R5are independently hydrogen or an alkyl, alkenyl, alkoxyalkyl, or arylgroup having a carbon number of 1 to 200; M is an alkali metal, alkalineearth metal, ammonium, alkyl-substituted ammonium, or aryl-substitutedammonium ion, each of m and n is an integer from 0 to 4, and the sum ofm and n is 1 or greater. When X is —OM and M is an alkaline earth metal,it will be understood that the metal may coordinate with one or twogroups having the indicated structure.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a hydroxy-functionaldendrimer, followed by conversion of any free carboxylic acid groupsfrom the anhydride to an acid salt (X is —OM), an ester (X is OR3), oran amide (X is —NR4R5) group.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a hydroxyalkylacrylate monomer, followed by radical-initiated polymerization of theresulting macromonomer and conversion of any free carboxylic acid groupsfrom the anhydride to an acid salt (X is OM), an ester (X is OR3), or anamide (X is —NR4R5) group.

In some aspects, the compound shown above is made by reacting apolyisobutylene-substituted succinic anhydride with a polyol, especiallyglycerol, followed by conversion of any free carboxylic acid groups fromthe anhydride to an acid salt (X is —OM), an ester (X is OR3), or anamide (X is —NR4R5) group.

Conversion of free carboxylic acid groups from the anhydride to an acidsalt, an ester, or an amide group (after reaction of thepolyisobutylene-substituted succinic anhydride) unexpectedly prevents anundesirable reverse reaction in which the anhydride reforms and thehydroxy-functional dendrimer, hydroxyalkyl acrylate copolymer, or polyolis eliminated. The undesirable reverse reaction has been found to occurat the elevated-temperature conditions in which the compositions arenormally used for dispersing asphaltenes or inhibiting asphaltenedeposition. Thus, converting the free carboxylic acid groups byneutralization or further derivatization to esters or amides improvesthe thermal stability of the products and extends their performance.

In some aspects, conversion of free carboxylic acid groups to a salt(i.e., neutralization) is accomplished by adding an inorganic or organicbase, e.g., sodium hydroxide, potassium hydroxide, potassium carbonate,sodium methoxide, potassium acetate, calcium hydroxide, sodiumsilicates, sodium phosphates, ammonia or a primary, secondary, ortertiary amine, a C₆-C₃₀ fatty amine, including aliphatic,cycloaliphatic, and aromatic amines. Tertiary amines are preferred;triethylamine is particularly preferred. Neutralization can also beaccomplished using solid bases such as basic alumina or basic ionexchange resins.

In some aspects, the free carboxylic acid groups are transformed intoester or amide groups using methods that are well known to those skilledin the art. Condensation of the acid with a primary or secondary amineprovides an amide, for instance. Reaction of the acid with an alcohol orphenol provides an ester.

By analyzing infrared spectra, and particularly the carbonyl region ofthe spectra, we surprisingly found that reaction products of PIBSA andhydroxy-functional reactants (dendrimers, polyols, or hydroxyacrylatemonomers) form the desired ring-opened product initially and are stableunder normal conditions. However, at the elevated temperatures (e.g.,80° C. to 250° C. or 100° C. to 200° C.) under which the compounds arenormally used for dispersing asphaltenes or inhibiting asphaltenedeposition, the anhydride ring can close and expulse the originalhydroxy-functional reactant. Consequently, the product can lose efficacyat elevated temperatures. To prevent this loss in efficacy, we foundthat a neutralizing agent such as triethylamine could be used tominimize or eliminate the undesirable side reaction. An alternative toneutralization, as discussed above, would be to convert the acid to anamide or ester to avoid the ring-closure side-reaction.

The reaction scheme below illustrates the effect of neutralization witha tertiary amine, where ROH refers to the hydroxy-functional reactant(e.g., dendrimer, polyol, hydroxyacrylate monomer) and PIB represents apolyisobutylene group substituted on the succinic anhydride reactant:

Wellbore Fluid Additives

Asphaltene inhibitors in accordance with the present disclosure may alsobe part of a multicomponent composition and combined with otherproduction chemicals such as demulsifiers, chaotropic agents,surfactants including charged and nonionic surfactants, sorbitan esters,amphoteric surfactants, and the like, viscosity reducers, mutualsolvents, corrosion inhibitors such as acid amine salts, imidazolinesand quaternary amines, demulsifiers such as alkoxylated resins,alkoxylated polyols and alkoxylated polyesters, paraffin inhibitors suchas ethylene vinyl acetate copolymers, alpha olefin maleate and furmaratepolyesters, and vinyl acetate, naphthenate inhibitors, and the like.

EXAMPLES

The present disclosure is further exemplified by the examples belowwhich are presented to illustrate certain specific embodiments of thedisclosure but are not intended to be construed so as to be restrictiveof the spirit and scope thereof.

Synthesis Examples

In a first example, an asphaltene inhibitor was prepared by reacting 1kDa PIBSA with a hydroxy-functional dendrimer. Compositions with variousPIBSA/dendrimer molar ratio were synthesized and denoted as Samples1a-1f as shown below in Table 1. Asphaltene inhibitors were alsoprepared by reacting PIBSA with hydroxyethyl methacrylate beforepolymerization, denoted Samples 2a-2c in Table 1, and by reacting PIBSAwith glycerol, denoted 3a-3b.

TABLE 1 Asphaltene Inhibitor Compositions Alkyl Succinic AnhydridePolyhydroxy Ratio Molecular Sample (ASA) component ASA:PN Weight 1aPIBSA dendrimer 1:1 — 1b PIBSA dendrimer 5:1 — 1c PIBSA dendrimer 10:1 — 1d PIBSA dendrimer 15:1  — 1e PIBSA dendrimer 20:1  — 1f PIBSAdendrimer 23:1  — 2a PIBSA hydroxyethyl 1:1 100 kDa methacrylate 2bPIBSA hydroxyethyl 1:1  55 kDa methacrylate 2c PIBSA hydroxyethyl 1:1 25 kDa methacrylate 3a PIBSA glycerol 3:2 — 3b PIBSA glycerol 3:2 —

Preparation of Sample 2(c)

Samples assayed also included polymeric asphaltene inhibitors preparedfrom a reaction of PIBSA with 2-hydroxyethyl methacrylate, which may besummarized as follows:

Sample 2(c) was prepared from polyisobutylene succinic anhydride (“PIBSA1000,” 8,834 kg, product of Innospec Fuel Specialties), which waspreheated to 80° C. and charged to a reaction vessel, followed bysolvent SOLVESSO™ 150 ND (5318 kg). The mixture was then heated to 60°C. 2-Hydroxyethyl methacrylate (“Visiomer® HEMA 98,” 902 kg, 1.05 eq.per eq. of PIBSA 1000, product of Evonik) was then added, and themixture was heated to 130° C. and held at 130° C. for 2 h. The reactionmixture was analyzed by infrared spectroscopy to follow thedisappearance of anhydride functionality. When the reaction wascomplete, the mixture was cooled to 100° C. Solvent SOLVESSO™ 150 ND(4386 kg) was added, followed by lauryl mercaptan (76 kg), and themixture was heated to 120° C. A mixture of t-butyl perbenzoate (134 kg)in SOLVESSO™ 150 ND (408 kg) was added slowly over 5 h at a constantrate while maintaining the reaction temperature at or below 120° C. Whenthe initiator addition was complete, the mixture was held at 120° C. for1 h. The reaction product had about 50% solids content.

GPC analysis of the reaction product showed two distinct populations ofproducts, with the higher molecular weight fraction (about 50%) havingnumber average molecular weight (M_(n))=16,800 and weight averagemolecular weight (M_(w))=28,200 (M_(w)/M_(n)=1.7). This fractionrepresents the expected homopolymer product. The lower molecular weightfraction (about 50%) has M_(n)=1800 and M_(w)=2900, which may representunconverted PIBSA.

Preparation of Sample 2(b)

Sample 2(b) was prepared from polyisobutylene succinic anhydride (“PIBSA1000,” 8,800 kg, product of Innospec Fuel Specialties) by preheating to80° C. and charging the compound to a reaction vessel, followed bySOLVESSO™ 150 ND (5298 kg). The mixture was heated to 60° C.2-Hydroxyethyl methacrylate (“Visiomer® HEMA 98,” 898 kg, 1.05 eq. pereq. of PIBSA 1000, product of Evonik) was added, and the mixture wasthen heated to 130° C. and held at 130° C. for 2 h. The reaction mixturewas analyzed by infrared spectroscopy to follow the disappearance ofanhydride functionality. When the reaction was complete, the mixture iscooled slightly to 120° C. A mixture of t-butyl perbenzoate (134 kg) inSOLVESSO™ 150 ND (408 kg) was added slowly over 5 h at a constant ratewhile maintaining the reaction temperature at or below 120° C. When theinitiator addition was complete, the mixture is held at 120° C. for 1 h.The reaction product was diluted with SOLVESSO™ 150 ND (4462 kg) toabout 50% solids content.

GPC analysis of the reaction product showed two distinct populations ofproducts, with the higher molecular weight fraction (about 60%) havingM_(n), =42,900 and M_(w)=92,200 (M_(w)/M_(n)=2.1). This fractionrepresented the expected homopolymer product. The lower molecular weightfraction (about 40%) had M_(n)=1960 and M_(w)=3550 and may representunconverted PIBSA.

Preparation of Sample Composition 1(e)

Sample 1(e) was prepared from BOLTORN™ H311 dendrimer (1,958 kg, 90%active in water, product of PERSTORP) which was preheated to 70° C. andpumped into a reaction vessel. SOLVESSO™ 150 ND solvent (8,000 kg,product of ExxonMobil Chemical) was added. The mixture was heated to100° C. and vacuum was applied to remove water until the water contentwas less than 0.10 wt. %; about 1800 g of solvent/water mixture isremoved. Polyisobutylene succinic anhydride (“PIBSA 1000,” 8,240 kg, 20equivalents per equivalent of BOLTORN™ H311 dendrimer, product ofInnospec Fuel Specialties) preheated to 80° C. was added to the reactor,and the mixture was heated to 120° C. and held for 2 h at 120° C.Infrared spectroscopy was used to monitor the reaction progress. Heatingfor another hour at 120° C. was used if needed. When the reaction wascomplete, the product was diluted with additional SOLVESSO™ 150 NDsolvent (3600 kg) to about 50% solids content.

Gel permeation chromatography (GPC) analysis of the reaction product wasperformed using a Varian PL-GPC-50 with Polypore columns, a refractiveindex detector, THF solvent (40 mg sample/mL), and polystyrenestandards. The chromatogram showed two distinct populations of products,with the higher molecular weight fraction having M_(n)=20,400;M_(W)=32,600 (M_(w)/M_(n)=1.6). This fraction also represented theexpected product. The lower molecular weight fraction had M_(n)=1600 andM_(w)=2570, which may represent unconverted PIBSA.

Application Example 1: Asphaltene dispersant testing

The stabilization/dispersion performance of the prepared asphalteneinhibitor compositions were evaluated under various tests that aredescribed below, with various crude oils. Asphaltene dispersant testingincluded evaluation of the asphaltene content of crude oils and theability of various products to disperse asphaltene. The procedurefollows method SPE 28972 asphaltene dispersant test (ADT). In the ADT,heptane is used as a non-polar solvent that promotes the agglomerationand precipitation of polar asphaltene. The test operates under theprinciple that effective asphaltene inhibitors will disperse andstabilize asphaltene in the non-polar solvent, and less precipitationrelative to a control without the asphaltene inhibitor will be observed.In this test, the petroleum fluid was diluted with xylene. Inhibitorconcentrations reported in the following tables are to be understood asthe amount of the selected asphaltene inhibitor with respect to theamount of crude oil.

Examples of asphaltene inhibitors were combined with five differenttypes of crude oil from distinct formations to study the effectivenessof the inhibitors with differing oil compositions. The results for eachinhibitor are shown below in Tables 2-6.

TABLE 2 Dispersion testing for oil sample 1 using testing method 1Asphaltene precipitation Inhibitor inhibition concentration (%) Sample(ppm) 2 hr 6 hr Blank 0 0 0 1b 150 86.7 76.9 1b 200 80 76.9 1c 150 66.784.6 1c 200 66.7 92.3 1d 150 61.1 66.7 1d 200 61.1 53.3 1e 150 100 76.91e 200 100 84.6 1e 150 61.1 33.3 1e 200 61.1 53.3 1f 150 50 46.7 1f 20055.6 53.3 2a 150 91.7 90 2a 200 97.2 96.7 2b 150 77.8 86.7 2b 200 83.393.3

TABLE 3 Dispersion testing for oil sample 2 using testing method 1Asphaltene precipitation Inhibitor inhibition concentration (%) Sample(ppm) 2 hr 6 hr Blank 0 0 0 Example 1c 200 97.2 85.7 Example 1d 150 5050 Example 1d 200 100 88.6 Example 1e 125 100 95 Example 1e 150 95 75Example 1e 200 100 100 Example 1f 125 50 37.5 Example 1f 150 75 62.5Example 1f 200 100 92.9 Example 2a 150 75 62.5 Example 2a 200 100 100Example 2b 200 88.9 78.6

TABLE 4 Dispersion testing for oil sample 3 using testing method 1Asphaltene precipitation Inhibitor inhibition concentration (%) Sample(ppm) 2 hr 6 hr Blank 0 0 0 Example 1b 50 100 80 Example 1c 150 100 100Example 1c 50 100 95 Example 1d 150 100 100 Example 1d 50 100 100Example 1e 150 100 100 Example 1e 50 100 100 Example 1f 150 100 100Example 1f 50 100 100 Example 2a 150 100 100 Example 2a 50 100 100Example 2b 150 100 100 Example 2b 50 100 80

TABLE 5 Dispersion testing for oil sample 4 using testing method 1Asphaltene precipitation Inhibitor inhibition concentration (%) Sample(ppm) 2 hr 6 hr Blank 0 0 0 Example 1b 25 100 0 Example 1b 25 40 25Example 1b 50 100 80 Example 1c 25 60 43.8 Example 1c 50 100 95 Example1c 50 80 50 Example 1c 75 77.8 64.3 Example 1c 100 90 85.7 Example 1e 2595 50 Example 1e 50 95 50 Example 1e 75 96.7 95.7 Example 1e 100 96.795.7

TABLE 6 Dispersion testing for oil sample 5 using testing method 1Asphaltene precipitation Inhibitor inhibition concentration (%) Sample(ppm) 2 hr 6 hr Blank 0 0 0 Example 1d 200 36.4 12.5 Example 1e 100 4525 Example 1e 200 100 93.8 Example 1e 300 100 90 Example 1f 200 95.5 75Example 1f 300 100 93.8 Example 2a 200 100 50 Example 2a 300 100 93.8Example 2b 200 100 75 Example 2b 300 100 93.8 Example 3a 200 100 68.8Example 3a 300 100 87.5 Example 3b 200 45 50 Example 3b 300 85 81.3

Application Example 2

In the next example, asphaltene inhibitor testing was monitored using anoptical turbidity scanner (FORMULACTION TURBISCAN™ MA2000) to compareproducts and concentrations in accordance with ASTM method D-7061. Thedispersant test measures sample asphaltene inhibitors for their abilityto maintain asphaltene compounds suspended in crude over a definedperiod, which may be used to determining the minimum concentration ofinhibitor to achieve similar results in the field and prevent depositionin process equipment.

During analysis, asphaltene inhibitor formulations were combined with asample of crude oil and the turbidity was measured over time as shown inFIG. 1. Crude oil 5 was also combined with various asphaltene inhibitorsand analyzed as shown in FIG. 2. A separate test was also conducted onsamples 2a and 2b at 150 ppm, resulting in <10% light transmission after24 hours test for each sample, respectively.

In the claims, means-plus-function clauses are intended to cover thestructures described herein as performing the recited function and notonly structural equivalents, but also equivalent structures. Thus,although a nail and a screw may not be structural equivalents in that anail employs a cylindrical surface to secure wooden parts together,whereas a screw employs a helical surface, in the environment offastening wooden parts, a nail and a screw may be equivalent structures.It is the express intention of the applicant not to invoke 35 U.S.C. §112(f) for any limitations of any of the claims herein, except for thosein which the claim expressly uses the words ‘means for’ together with anassociated function.

1. A composition comprising a reaction product of apolyisobutylene-substituted succinic anhydride and a hydroxy-functionaldendrimer, wherein the molar ratio of polyisobutylene-substitutedsuccinic anhydride to hydroxy-functional dendrimer is within the rangeof 10:1 to 30:1.
 2. A composition comprising a compound of the formula:

wherein R1 is an alkyl chain having a carbon number of greater than 40to 200, R2 is a multiester group, X is —OR3 or —NR4R5 or —OM, wherein R3is an alkyl or aryl group having a carbon number of 1 to 200, R4 and R5are independently hydrogen or an alkyl, alkenyl, alkoxyalkyl, or arylgroup having a carbon number of 1 to 200, M is an alkali metal, alkalineearth metal, ammonium, alkyl-substituted ammonium, or aryl-substitutedammonium, each of m and n is an integer from 0 to 4, and the sum of mand n is 1 or greater.
 3. The composition of claim 2, wherein R1 is analkyl chain having a carbon number in the range of 50 to 100, X is —OM,and m+n=1.
 4. The composition of claim 3, wherein R1 is an alkyl chainhaving a carbon number in the range of 60 to
 75. 5. The composition ofclaim 2, wherein the multiester group is a dendrimeric multiestercomprising 8 to 50 ester groups.
 6. The composition of claim 2, whereinthe compound has a weight average molecular weight in the range of 900to 100,000 Da.
 7. The composition of claim 2 wherein the compound has aweight average molecular weight in the range of 10,000 to 50,000 Da. 8.The composition of claim 2, wherein R1 is an alkyl chain generated fromthe reaction of one or more monomers selected from a group consisting ofethylene, propene, butylene, and isobutylene.
 9. The composition ofclaim 2, wherein the multiester group is a dendrimeric multiestercomprising a polyalcohol core and one or more generations of2,2-dimethylolpropionic acid.
 10. The composition of claim 9, whereinthe polyalcohol core is pentaerythritol.
 11. The composition of claim 2,wherein the compound is made by reacting a polyisobutylene-substitutedsuccinic anhydride with a hydroxy-functional dendrimer, and conversionof any free carboxylic acid groups from the anhydride to an acid salt,an ester, or an amide group.
 12. The composition of claim 11, whereinthe molar ratio of polyisobutylene-substituted succinic anhydride tohydroxy-functional dendrimer is within the range of 10:1 to 30:1. 13.The composition of claim 11, wherein the molar ratio ofpolyisobutylene-substituted succinic anhydride to hydroxy-functionaldendrimer is within the range of 15:1 to 25:1.
 14. The composition ofclaim 11, wherein the molar ratio of polyisobutylene-substitutedsuccinic anhydride to hydroxy-functional dendrimer is about 20:1. 15.The composition of claim 11, wherein the polyisobutylene-substitutedsuccinic anhydride has a weight average molecular weight within therange of 500 to 10,000 Da.
 16. The composition of claim 11, wherein thepolyisobutylene-substituted succinic anhydride has a weight averagemolecular weight within the range of 800 to 3,500 Da.
 17. Thecomposition of claim 11, wherein the hydroxy-functional dendrimer has 23free hydroxyl groups prior to reaction with thepolyisobutylene-substituted succinic anhydride.
 18. The composition ofclaim 11, wherein the hydroxy-functional dendrimer, prior to reactionwith the polyisobutylene-substituted succinic anhydride, has a hydroxylvalue within the range of 230 to 260 mg KOH/g and a weight-averagemolecular weight within the range of 5,500 Da to 6,000 Da.
 19. Thecomposition of claim 2, further comprising 1 to 90 v %, based on theamount of composition, of an aromatic solvent.
 20. The composition ofclaim 19, wherein the aromatic solvent is selected from the groupconsisting of benzene, toluene, xylenes, ethylbenzene, cumene,mesitylene, and mixtures thereof.
 21. The composition of claim 2prepared by reacting polyisobutylene succinic anhydride with ahydroxyalkyl acrylate monomer, followed by radical-initiatedpolymerization of the resulting macromonomer and conversion of any freecarboxylic acid groups from the anhydride to an acid salt, an ester, oran amide group.
 22. The composition of claim 21 wherein the hydroxyalkylacrylate monomer is 2-hydroxyethyl acrylate or 2-hydroxyethylmethacrylate.
 23. The composition of claim 2 prepared by reactingpolyisobutylene succinic anhydride with a polyol, and conversion of anyfree carboxylic acid groups from the anhydride to an acid salt, anester, or an amide group.
 24. The composition of claim 23 wherein thepolyol is glycerol.